Cathode ray tube system



Apmll 17, 1962 H- P. GROLL ET AL 3,030,443

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Jn ven 2 0 r5 HORST GROLL a PATENT 4 April! 17, 1962 H. P. GROLL ETAL CATHODE RAY TUBE SYSTEM Filed Oct. 14, 1959 Fl6.30 H H H H Fig. 5

4 Sheets-Sheet 3 Jnvenfons.

HORST GROLL 8 KLAU LAIVGE M PATENT AGENT April! 17, 1962 H. P. GROLL ET AL 3,030,443

CATHODE RAY TUBE SYSTEM Filed Oct. 14, 1959 4 Sheets-Sheet 4 Fig. 4

Jn van in rs: HORST mou a KLAUS LANGE' BY PATENT AGE/V7 Unite The present invention relates to a system of cathode ray tubes and, more particularly, to means for adding visible markers onto the screen of a cathode ray tube at a primary receiver, and wherein the same markers are also made visible on one or more additional or secondary picture-tube receiver screens.

The problem arises, for example, when radar images are reproduced remotely from the primary receiver. In such case, it is often necessary to mark a particular target appearing on the screen by so-called tactical markers, such as arrows, circles, numbers or letters associated with the image of a particular target. This marker must then also appear on the presentation screens of secondary receivers to facilitate the identification and pursuit of one or more particular targets. Thus, it becomes very important that these markers can be added very quickly, and that they can be erased very quickly.

It has been known in the art to solve the problem outlined above by superimposing a transparent plate over the primary receiver screen, whereby the position of the plate is accurately located. The markers are applied as opaque writing on the plate, for example, by means of a grease pencil. The plate then is removed and positioned in front of a photoelectric scanner. The position of the plate in front of the scanner corresponds exactly with its prior position in front of the video screen. The photoelectric flying-spot scanner is controlled in synchronism with the radar device. The signals derived from the photoelectric scanner are then added to the radar receiver signals and they produce on the screens of the secondary receivers images which are a combination of the radar target images and the marker images.

The device outlined above has several disadvantages. The positions of the plates carrying the additional markers have to be adjusted in front of the primary screen as well as in front of the scanner with extreme accuracy in orderto obtain faultless superposition of targets and markers on the secondary video screens. Furthermore, the removal of the plate from the primary video screen and its positioning in front of the scanner takes some time. Thus, there is a certain delay before the markers will appear on the secondary video screens. When the target moves fast, such as a fast aeroplane, the entire arrangement might turn out to be useless or even misleading.

It is, therefore, an object of the present invention to provide a new and improved device for adding video markers on cathode ray tube-screen images without the deficiencies outlined above.

It is another object of the present invention to provide new and improved means, whereby a marker indicated or placed on a primary video screen can be transmitted and reproduced on secondary video screens together with the primary image without any delay.

It is a further object of the invention to fix a transparent plate in front of a primary video screen and markers may be entered thereon as opaque lines, spots and/ or areas.

Alternatively, the markers may be placed directly on the outer surface of the cathode ray tube screen. A photoelectric detector positioned in front thereof ob serves the plate and transmits a signal or a train of signals to the secondary receivers. The photoelectric device may be a photoelectric cell or a photo-multiplier, including the necessary amplifier circuit and, if desired, an optical system. A mixing device is positioned between the pri mary receiver and the secondary receivers. The primary video signal as well as the output signal of the photoelectric detector are fed into the mixing device and the output thereof is connected to the secondary receivers.

Let it be assumed that the screen of the primary receiver has a fiuorescing layer with but very short persistence, such as is the case, for example, in ordinary TV tubes. It will readily be seen that the arrangement according to the present invention, without additional scanning means, allows a signal to be obtained which contains the original video signals as well as signals which correspond to the additional markers. Without any marker, thephoto signal derived from the photoelectric detector would correspond exactly to the initial video signal as fed into the primary receiver, because at every moment, only the particular area of the screen on which the cathode ray of the receiver tube impinges is fluorescing. This happens, regardless of which particular area is hit at any particular moment.

The successive video signals controlling the brightness of the spot are reproduced at the photoelectric input and, therefore, at the output of the photoelectric detector. Thus, when markers are written on the transparent video screen on the outside thereof, or on a plate positioned in front of the screen, the amplitude of the signal in the photoelectric detector is always reduced to zero, i.e., when;

improved when the persistence of the primary screen is very short.

The device according to the invention is also suitablefor adding of additional markers on radar screens in PPI (plan position indicator) presentation. In this case, it has to be considered that the image on the screen is produced relatively slowly, because the radially directed line traced by the cathode ray rotates on the screen in synchronism with the rotating radar antenna. For observation of the complete picture, screens have then to be used which have longer persistence, at least for the period of 7 time required for the rotating line to complete one revolution. However, the scanning of the markers to be added is based on the proposition that every area on the screen hit by the cathode ray beam has almost no persistence and acts only very briefly on the photo cell positioned in front of the screen, because the position of every image dot on the secondary screens produced by the output signal of the photo cell is directly in coincidence with the time and the period of the fluorescing flow of the image dots on the video screen of the primary receiver.

These conditions appear to be compatible at first glance. They can, for example, be reconciled by usinga' screen having a very bright fluorescence under the direct impact of an electron beam, but wherein the afterglow of the fluorescence, i.e., the persistence itself, is at a relative ly low level. The photo cell would register only the first" impact produced when the cathode ray hits an area of the video screen, but it would not register the afterglow.

In this case, the signal to noise ratio of the signals repre-" senting the added markers is relatively small, but can be made useful by means of limiter stages.

Another modification of the principal embodiment with in the scope of the invention takes care of the two abovementioned conditions in radar devices in another manner. A primary video screen can be used in which fluorescence occurs at one Wave length, for example, as blue, while. the afterglow phosphorescence occurs as green-yellow. The photoelectric device then needs only to be sensitive to blue light, while all other colors, particularly, yellowgreen, are suppressed.

For example, a filter may be placed in front of the photo cell, said filter passing blue light only. In addition, or as an alternative, a photo-sensitive device may be used, having a maximum sensitivity at the fluorescence color of the video screen.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

In the drawings:

FIGURE 1 is a block-circuit diagram of a first embodiment of the invention;

FIGURE 2 is a block-circuit diagram of a modification of the embodiment shown in FIGURE 1;

FIGURES 3a and 3g show waveforms of various signals as they appear at different points in the circuit of FIGURE 2;

FIGURE: 4 illustratesschematically aside view of a structural detail of an element used in FIGURES l and 2-;

FIGURE 5 is a side view of another element used in FIGURES} and 2-; and

FIGURE 6' is a front view of the element shown in FIGURE 5 with a slight simplification of the illustration.

Referring in detail to the drawings, FIGURE 1 shows a pulse generator 1 for a radar system, said generator feeding pulse control signals into a transmitter 2; The generator pulse signals are also used as sweep synchroniz ing pulses for the receivers, as will be explained below. The transmitter 2 is connected toan antenna duplexer 3 which, in turn, is connected to an antenna 5 via an antenna control device 4. The antenna 5- is driven by a motor 6 and rotates continuously about a vertical axis. The rotation may be carried out at ten revolutions per minute. The antenna control device 4 feeds a signal into a line 7, which signal is indicative of the momentary angular position of the antenna and is used to control the deflection coils of the radar presentation. Thissignal will be designated in the following briefly as the angular signal. However, this signal is" not essential for the invention. The radar signals which are reflected by a target are received by the antenna 5- and are" fed into a receiver circuit 8 via the antenna duplexer 3. The output of a. receiver circuit 8 appears on a line 9, said output representing the video signals, angular signal, and synchronizing pulses. the video receiver indicator 11, the primary indicator having. a primary video screen 12 on which a radar image or picture will be presented.

In order to reduce the usual band width, it is possibleto use a device for frequency band width compression of the video signal. Devices of this kind have been known and need no further discussion. They can be inserted into the lines to the secondary receivers. However, it is more advantageous to insert these compressing circuits before the signals reach the primary receiver 11.

Box 13 indicates such a compression circuit. The entire arrangement of primary and secondary video devices, asv will be explained below, can be made fairly simple, due to the relatively low frequencies which leave the compression circuit 13 when the latter is placed as shown in the drawing. In particular, the picture fidelity and the The latter are fed via a line into sharpness may be improved. However, the operation of the following circuit elements does not depend on the use of a compression circuit 13 and this circuit may be omitted. Thus, when, in the following, reference is made to video signal, this is to be understood to comprise a signal with or without frequency band-width compression.

The video indicator 11 includes all of the circuits and auxiliary devices, such as drives and deflection means, necessary for a PPI presentation. The fluorescent layer of the video screen 12 of the picture tube of the indicator 11 fluoresccs blue upon being hit by the cathode ray beam inside of the picture tube and it has a phosphorescing afterglow of green-yellow. .A photoelectric device 14, such as a photocell, is disposed and secured in front of the video screen 12. The photo cell 14 converts the light signals appearing on the screen 12 as fluorescing dots into electrical signals. Markers, such as 15, are placed on the outside of the screen 12 and are modifying the florescing picture as seen by the photocell 14. Suitably, a light-hood 16 is provided in front of the cell 14, i.e., between the latter and the video screen 12. The purpose of the light-hood 16 will be explained later with reference to FIGURES 5 and 6.

The output of the photo cell 14 is fed into an amplifier 17 which, in turn, feeds an amplified output signal to a mixer 19 via a line 1-8. The amplified photo signal is mixed additively in the mixer 19 with the video signal coming from the receiver 8. The video signal appears in line 9" combined with the signal from the photoelectric detector. The signal in line 9" and the angular signal and the synchronizing pulse are now fed to secondary indicators, such as 21, having a video screen 22. Lines 7' and 10 are the respective continuations of lines 7 and 10' for angular signal and synchronizing pulses, respectively.

The primary video indicator 11 can be operated in two different manners. In the first mode of operation, it is assumed that the image on the screen is traced in the usual manner, i.e., as bright dots on dark background. This may be called positive. In this case, the basic background brightness of the screen is adjusted in such a manner, that the entire screen fiuoresces weakly, even where the radar signal is zero. When the markers 15, to be added to the picture, are written directly on the outer glass surface of the picture screen 12 or on an additional front plate mounted adjacent this screen 12, a certain portion of the fluorescing light is masked when a grease pencil, producing an opaque marker, is used. The photo cell 14 then produces a signal which combines the various brightness increases representing the image on the fluorescing video screen 12 withthe reduction of brightness produced by the markers 15, partially masking the fl uorescing screen.

Without any additional provisions, the markers wouldbe reproduced as dark markers on the video screen 22 of the secondary indicator 21. The signals corresponding to the initial images reproduced on the primary video screen are scanned by photocell 14 as signals of a brightness exceeding the overall background brightness as adjusted on the indicator 11. The signals corresponding to the markers are signals having an amplitude which is lower than that corresponding to the background brightness. Thus, in the photo cell 14, video signals and marker signals are of opposite polarity. This, in turn, means that the signals can be separated, for example, by means of an amplitude limiter. The marker signals can then be separated from the video signals of the original radar image and can feed the former to a reversing stage whtich can be a component of the mixing stage 19. The markers now will appear as bright images on the secondary screen 22.

According to another possible mode of operation of the device disclosed in FIGURE 1, a negative image is projected on the radar screen 12, i.e., a dark image on a bright background. In this case, the image on the primary screen 12 and the added markers 15 have the same polarity in the photo cell 14. Thus, it is possible to incorporate in the secondary receiver an inversion stage producing simultaneously a positive picture of the initial video image and the markers on screen 22.

In a modificatiton of the device shown in FIGURE 1, the mixer stage 19 and the line 9 may be omitted and, instead, line 18 may be connected to the video signal input of secondary indicator 21. Thus, the secondary receiver would obtain its video signal directly from the photo cell 14.

With reference to the device of FIGURE 1, it has been found advantageous to first feed the output of the amplifier 17 into a difierentiatiug stage 20 and then to feed the output of the latter to the mixer 19. With such provision, there can be avoided disturbances produced by the hand or the head of the person writing the markers 15 on the screen 12 and, thereby, frequently coming into the scanning area of the photo cell 14. Due to the diiferentiating stage 20, only the edges or boundaries of the markers 15 are transmitted to the secondary indicator. This, by experience, has been found suflicient, particularly, when the markers are of small size. A skillful observer of the primary screen 12 will put the markers on or off this screen in such a manner, that his hand will only briefly come into the range of the slowly rotating PPI line.

Another advantage of the use of a differentiating stage for the output signals of the amplifier 17 lies in the substantial decrease of the influence of external disturbing light affecting the photo cell 14. Daylight or room lamps operated with DC. will be rendered completely ineffective by the difierentiating stage unless the photo element is displaced beyond its operating range, in which case, of course, the output of the differentiating stage would be always zero. The influence of A.C.-supplied room lamps is sufficiently but incompletely eliminated.

The amplifier 17 is suitably provided with an A.G.C. or any other kind of automatic control to reduce variations of its operation point which might occur when the ambient light varies.

FIGURE 2 illustrates a device according to this invention, in which the cooperation of the primary video indicator 11 and the photoelectric device 14 is modified with respect to the system shown in FIGURE 1. The reproduction of the primary image is separated from the addition of markers even though only one primary video screen is used. This is obtained by tracing only every other line on the primary screen carrying the video sig nal, while the intermediate lines are displayed with a medium, uniform brightness. These lines are then used for the detection of the markers. This method has the advantage that even a relatively bright environment will not disturb the superpositioning of the markers upon the video signals according to the invention.

The elements in FIGURE 2 corresponding to similar elements of the device shown in FIGURE I bear like reference numerals. This is particularly true for the elements 1 through 9, denoting the transmitter, the antenna and the control stages of the transmitter. Also, the frequency band-width compressor 13, if any, the primary indicator 11, the secondary indicator 21 and the photo cell 14 with its amplifier 17 are not modified.

A synchronizing pulse a, FIGURE 3a, from line 10' is fed into a generator 23 (FIGURE 2) for producing a square wave output voltage. The shaped synchronizing pulse, i.e., the output of the generator 23, is fed into electronic switches 24 and 25 via lines 26 and 27, respecti-tvely. The switch 24 is connected between the video input line 9' and the primary indicator 11, while the switch 25 is inserted in the line 18 and, thus, is supplied from the output of the amplifier 17. The polarities of the square wave signals fed into the lines 26 and 27 are opposite as indicated in FIGURES 3b and 3c.

As can be seen, the voltages shown in FIGURES 3b and 3c have a frequency which is twice the frequency of the synchronizing pulses shown in FIGURE 3a. The switch 24 operates in such a manner, that it is open during the negative half wave of its operating voltage (FIG- URE 3c). Thus, video signal d (FIGURE 3d) passes through the line 9 into the indicator 11. During the positive half wave of voltage c, the indicator obtains only a constant control voltage (time interval t in FIG- URE 3:2) for controlling the intensity of the cathode ray at a predetermined lever, providing during this period of time a constant brightness of the respective picture-tracing line. This is indicated in FIGURE 3e, showing the signal which appears in line 9" connecting the switch 24 to the indicator 11. If only the additional devices mentioned so far were present, i.e., if the switch 26 were absent, there would be an improvement with respect to the device shown in FIGURE 1, because the disturbance amplitude would be reduced. However, there is obtained a broadening of the video signals as detected by the photo cell and fed into the secondary receiver, due to an increase of the screen phosphorescence. The additional use of the switch 25 remedies the lastmentioned deficiency. This switch 25 is controlled by the voltage shown in FIGURE 3b, so as to turn off the output of the amplifier 17 during the periods when video signals are detected by photo cell 14 (time periods in FIGURE 32). The output of the switch 25 as fed into the line 18 thus includes only the signals which correspond to the markers as scanned by the photo cell, 14 during the time intervals when the video signal was blacked out by the switch 24 duringthe time t as shown in FIGURE 3 f. In the mixing stage 19, the complete video signal of line 9 is combined with the signals of line 18' which are exclusively associated with the markers 15 as written on the outside of the screen 12.

The combined signals are shown in FIGURE 3g and they appear in the input line 9" of the indiactor 21. The train of signals according to FIGURE 3g is based on the assumption that the difierentiation stage 20 is omitted. In the presence of this stage 20, as indicated in FIGURE 2, the pulses representing the markers are modified to coinprise pulses representing the leading and trailing edge thereof.

The device of FIGURE 2 differs from that shown in FIGURE 1 in that in the former, the mixing stage is associated with the location of the secondary indicator 21.

In this case, the communication lines for video signals.

have to be separated from the marker signals. In case of communication by radio, another channel is necessary. This has the advantage that the observer of the secondary screen can adjust separately the amplitude of the video signal and the amplitude of the marker signal. The observer of the secondary screen even has the choice of' observing the image thereon with or without markers. It is understood that the particular location of the mixer stage 19 has no influence on the principal operation of the entire device. Such location of the mixer 19 may also be used in the embodiment of FIGURE 1.

FIGURE 4 illustrates an advantageous position of the photoelectric device 14 with respect to the video indicator 11. The covers for the indicator 11 and the cell 14 are omitted to facilitate the understanding of the illustration. A frame 28 for the positive tube 12 is shown in cross section. The indicator 11 is positioned so that the screen 12 is horizontal and is spaced above the floor corresponding to the conventional height of a table. A glass plate 29 is mounted in the frame 28 closely above the screen 12. A housing 30 for the photo cell 14 is suspended from the ceiling of the room in which the primary indicator 11 is placed, so that the housing 30 does not hinder the observer. The position as shown is of great advantage, because the markers may not only be written onto the plate 29 with a grease pencil, but masks may be used, for example, of arrows, letters, and numbers made, i.e., cut out, of opaque material, for the fluorescence of the screen 12, said masks being simply laid on the plate 29 and then being shifted thereon as desired according to the movement of their associated targets. The removal of such markers, of course, is much faster, as they can be simply removed, that when the grease markers have to be erased by means of a cloth soaked with a desolving agent. In the case of several observers watching the screen, vertical positioning of the screen 12 is pereferable, even if only one observer writes the markers or employs masks which may be connected to the glass plate by means of suction cups.

The photo cell 14 should be influenced by as little disturbing light as possible and only light from screen 12 should reach the cell. The portion of such light entering the cell 14 should be as large as possible. To accomplish this, lens and/or mirror means of known types can be used, said means casting an image of the screen 12 onto the photo cathode of cell 14. However, such means complicate the whole device, whereby it has to be considered that photo cathodes usually do not have a uniform sensitivity all over their surface. Therefore, these optical means appear to be not essential.

To further improve the systems described, it is suggested to mount a hood 16 with an inner mirror surface in front of the photo cell 14, whereby the large opening of the funnel faces the video screen 12. The diameter of the smaller opening adjacent the cell 14 should correspond to the size of the photo cathode. The optimum length of the hood 16 with respect to its opening and the necessary inclination or curvature of the mirrored inside surface can be determined by the known laws of optics. It has been found experimentally, that a funnel made of straight boundary surfaces, asshown in FIGURES and 6, having the shape of a truncated pyramid, can yield a light increase by the factor 10. Disturbing light coming from the side leaves the hood after several reflections, and hardly any of this light reaches the photo cathode.

The mirroring surface of the hood' has the further advantage that saicl surface can be used for a certain color selection. When the mirroring surface, for example, is made of chromium, the preferred blueish reflection is obtained, while yellow is more or less absorbed. This feature facilitates the separation of the blue fluorescing light from the yellow phosphorescence. As shown in FIGURE 5, a color filter 31 may be placed in front of the hood 16.

It is of further advantage to provide the power supply in the housing 30 when the photoelectric device is a photo multiplier requiring a high anode voltage. In this case, the use of long high voltage power cables is avoided.

We claim:

1. A device for adding visible markers to the image to be reproduced by cathode ray tubes of video indicators comprising, means to produce video signals; means to produce alternating pulses corresponding to alternate line sweeps in said video signals; a first indicator having a brightness gating means; means to feed said video signal to said gating means; means to alternately open and close said gating means in synchronism with said alternating pulses during successive line sweeps of said video signals; means to feed the output of said gating means to said first indicator whereby every alternate line is modulated with said video signals and the intermediate lines are traced at a constant brightness; transparent means in front of said screen to carry opaque markers; photoelectric detector means to observe said screen and said markers through said transparent means and producing an output only during intervals when the lines are traced at constant brightness; means to mixsaid lastmentioned output and said video signals; and a second indicator having its intensity controlled by the output of said lastmentioned means.

2. A device as set forth in claim 1, wherein said first indicator includes a cathode ray tube the color wave" length of the fluorescent component thereof differing substantially from the color wave length of the phosphorescent component.

3. A device as set forth in claim 2, comprising in addition, a tapered light-guiding hood having an inner mirrored surface positioned in front of said photoelectric means with its smaller opening thereadjacent, the larger opening of said hood facing. the video screen of said first indicator.

4. In a device according to claim 3, saidhood being a truncated pyramid.

5. In a device according to claim 3, said mirrored surface of said hood having a preferred reflection in the color of the fluorescence and a reduced reflection in the color of the phosphorescence of Said screen of said first indicator.

6. In a device as set forth in claim 1, a second gating means for controlling the passage of the output fed from said photoelectric detector means to said mixing means; and means to open said second gating means when said firstmentioned gating means is closed and vice versa.

References Citedin the file of this patent UNITED STATES PATENTS 2,483,432 Richardson Oct. 4, 1949 2,522,528 McNally Sept. 19, 1950 2,622,240 Fleming-Williams Dec. 16, 1952 2,758,298 Sunstein Aug. 7, 1955 2,798,901 Harter July 9, 1957 2,954,427 Covely Sept. 27, 1960 

